Code

Sample C (MCU API) and Python (MPU API) code for FlexConnect.

FlexConnect MCU library

The FlexConnect SPI framing library is provided in the repository lib/ directory:

• lib/flexconnect.h — API header
• lib/flexconnect.o — prebuilt object file (link at build time)

Add lib/ to your include path and link flexconnect.o into your firmware project. The FlexConnect IMU example demonstrates end-to-end usage on an S32K3 MCU.

Typical SPI exchange cycle

On each SPI transfer to the MPU:

1. Queue outbound CAN messages with flx_pushToBuffer.
2. Serialize the transmit buffer with flx_txDataPrep.
3. Run the SPI transfer (driver-specific).
4. Decode the receive buffer with flx_rxDataPrep.

The IMU example runs this cycle every 100 ms in Exec_100ms() :

// Push SPI data to Flexconnect Tx buffer
flx_pushToBuffer(7u, IMU_Bytes_A_ID, 8u, IMU_Bytes_A);
flx_pushToBuffer(7u, IMU_Bytes_B_ID, 8u, IMU_Bytes_B);

// Prepare Tx data
flx_txDataPrep(FLX_TxData, FLX_TransferSize);
Spi_SetupEB(SpiConf_SpiChannel_SpiChannel_MPU, FLX_TxData, FLX_RxData, FLX_TransferSize);

// Transmit data over SPI
Spi_SyncTransmit(SpiConf_SpiSequence_SpiSequence_MPU);

// Process Rx data
FLX_Rx_DataValid = flx_rxDataPrep(FLX_RxData, &FLX_Rx_Channel, &FLX_Rx_ID, &FLX_Rx_DLC, FLX_Rx_Payload, FLX_TransferSize);

After a successful receive, the example toggles an LED when FLX_Rx_DataValid is true.

SPI transfer size (FLX_TransferSize)

FLX_TransferSize is the number of bytes exchanged on each SPI transfer between the MCU and MPU. The FlexConnect frame packs multiple CAN messages into a single transfer, plus a small header:

The transfer size is therefore 13 × 16 + 9 = 217 bytes. The IMU example defines this as:

#define FLX_MessageSize 13U
#define FLX_MessagesPerTransfer 16U
#define FLX_TransferOverhead 9U
#define FLX_TransferSize (FLX_MessageSize * FLX_MessagesPerTransfer + FLX_TransferOverhead)

Pass this value as spi_sz to flx_txDataPrep and flx_rxDataPrep, and use the same length when configuring the SPI driver for the MPU channel.

API reference

flx_pushToBuffer

Queues a CAN message for transmission to the MPU on the next SPI exchange.

Returns a flx_bufferStat value: FLX_BUFF_OK, FLX_BUFF_FULL, FLX_BUFF_BUSY, or FLX_BUFF_ERROR.

In the IMU example, two 8-byte IMU frames are queued on channel 7 before each transfer:

flx_pushToBuffer(7u, IMU_Bytes_A_ID, 8u, IMU_Bytes_A);
flx_pushToBuffer(7u, IMU_Bytes_B_ID, 8u, IMU_Bytes_B);

Call this as often as needed between SPI transfers. Messages that do not fit in the next frame remain queued for later exchanges.

flx_txDataPrep

Builds the next SPI transmit buffer from queued outbound messages and removes any messages included in that buffer. If no messages are queued, writes an empty transfer.

flx_txDataPrep(FLX_TxData, FLX_TransferSize);

FLX_TransferSize is 217 bytes (13 × 16 + 9) in the IMU example. Pass the resulting buffer to your SPI driver before starting the transfer.

flx_rxDataPrep

Decodes a received FlexConnect SPI transfer. On success, writes the CAN channel, identifier, data length, and payload, and returns true. Returns false when no valid message is present.

FLX_Rx_DataValid = flx_rxDataPrep(FLX_RxData, &FLX_Rx_Channel, &FLX_Rx_ID, &FLX_Rx_DLC, FLX_Rx_Payload, FLX_TransferSize);

if (FLX_Rx_DataValid)
{
    // handle inbound message from MPU
}

flx_getBufferFullCount

Returns the number of flx_pushToBuffer calls rejected because the outbound buffer was full since reset. Use this to detect when the MCU is producing messages faster than the SPI link can carry them.

uint16_t fullCount = flx_getBufferFullCount();

flx_getBufferBusyCount

Returns the number of operations rejected because the buffer was locked by another operation since reset. Use this to detect concurrent access to the message buffer.

uint16_t busyCount = flx_getBufferBusyCount();